The present invention relates to an enhanced micropump for the nebulization of fluids.
A micropump of this kind is suitable for mounting on a cap for glass or plastic bottles destined to contain perfumes or other substances which, in relation to their specific use, require nebulization.
Generally, this type of micropump comprises a pump body and a set of hollow stern and piston such as to constitute together with the body a "metering chamber";0 the exit duct for the fluid includes the longitudinal cavity of the hollow stem, a so called "compression pre-chamber" obtained in a dispensing push-button and at least one passage from this "compression pre-chamber" to a "vortex chamber" of a nebulization element fitted with related orifice. The stem and piston set is movable within the body thanks to the antagonistic action between the dispensing push-button and a helical spring, abutting in the "metering chamber" against the front end of the stem. The stem and the piston of the set are, themselves, mutually movable to uncover one or more through holes obtained in the stem, at the moment the dispensing push-button is pressed to allow the fluid to be nebulized to pass from the "metering chamber" into the fluid exit duct.
In a system of this type the pressure inside the "metering chamber" necessary to obtain a correct nebulization is guaranteed by a valve, which could be called "minimum pressure" valve, obtained with the aforesaid piston and a "pre-loading" spring abutted between the piston and a flange provided on the stem inside the pump body. Such "minimum pressure" valve determines the threshold pressure which must exist in the "metering chamber" for the through holes of the stem to be uncovered, and the pressurized fluid to travel through the longitudinal cavity of the stem, reach the "compression pre-chamber", be accelerated and exit from the orifice of the nebulization element, creating the nebulization cone.
In the prior art system the correct nebulization requires the fluid to reach the "compression pre-chamber" with sufficient pressure to be accelerated adequately. This depends mainly: 1) on the pre-load imparted by the "pre-loading" spring in relation to the surface area of the inner straight section of the pump body, 2) on the head losses the fluid undergoes in its exit duct, and 3) on the "sensitivity" of the "minimum pressure" valve. On the basis of the first factor mentioned, it is evident that, the spring pre-load value being equal, the smaller the inner diameter of the pump body, the greater the pressure threshold value will be and the better the nebulization will be. On the other hand it is not advantageous to increase the spring pre-load excessively since, for the same inner diameter of the body, the force that the user must impart to the dispensing push-button would be excessive and the use of the device would not be very comfortable.
For the second factor, the smaller the head losses, with the threshold pressure being equal, the more pressure the fluid retains in correspondence with the "compression pre-chamber".
Lastly, the "sensitivity" of the "minimum pressure" valve is its ability to shut the passage when the pressure in the "metering chamber" drops below the threshold value. This generally occurs when the speed with which the dispensing push-button, and thus the stem and piston set, is lowered, is slow. If the "minimum pressure" valve is not very sensitive, the fluid reaches the nebulization clement with insufficient pressure for adequate nebulization.
On the basis of the first factor mentioned above, the prior art pump presents, due to a distinct construction of stem and piston, the drawback of having a pump body with an excessive cross section, and therefore insufficient threshold pressure values are determined with the need to increase spring pre-load.
With regard to the second factor in relation to the prior art pump, since the "minimum pressure" valve, comprised by the piston which covers and, vice versa, uncovers the holes by means of the "pre-loading" spring, is situated away from the "compression pre-chamber", the head losses, i.e. Those along the hollow stem, are significant, and hence pressure in the "compression pre-chamber" can be insufficient.
With reference to the sensitivity of the prior art pump, the friction forces generated between the outer lip of the piston and the inner surface of the pump body tend to hamper the correct closure of the piston pushed by the pre-loading spring, even when pressure in the duct would actually be lower than its threshold value.
Pump systems already exist which use micro-springs associated to micro-shutters positioned inside the cylindrical duct of the stem in the vicinity of the nebulization element, which acting on small sections, maximize, other conditions being equal, the dispensing pressure value. These systems, being independent of friction resistance, also present high "sensitivity".
Although they are able to obviate all drawbacks, the aforementioned systems are particularly complex and, given their small size, the production of their components and their assembly, especially in terms of dimensional precision and repeatability, are very onerous, and thus entail an increase of the final cost of the pumps and of the containers whereto they are applied.